Development of a chronic hepatitis B infection is revealed by a changed antigen-antibody profile: the two antigens HBs and HBc (and raised transaminases) persist for over six months, whereby antibodies to HBe and HBs are not produced. A subsequent "late seroconversion" of HBe antigen to anti-HBe antibodies supports a better prognosis. Thorough clarification of chronic cases must include either immunohistological testing for HBV antigens in liver biopsies or PCR testing for the presence of viral DNA, and thus Dane particles, in patient serum.
Epidemiology and prevention. Humans are the sole reservoir of HBV. Transmission is parenteral, either with blood or body fluids containing HBV (sexual intercourse) that come into contact with mucosa, lesions, or microlesions in the skin. In transmission by blood, the tiniest amounts contaminating syringe needles, ear-piercing needles, tattooing instruments, etc. suffice to produce an infection. Hepatitis B infections from blood transfusions have been greatly reduced by thorough screening of blood donors for HBs antigens, despite which patients receiving multiple transfusions or dialysis remain a high-risk group.
Another high-risk group includes all healthcare workers with regular blood contact. All blood samples must be considered potentially infectious and handled only with disposable gloves. Addicts who inject drugs with needles are also obviously exposed to a very high level of risk.
Since no effective chemotherapy against HBV has been developed to date, the WHO recommends general hepatitis B prophylaxis in the form of active immunization with HBs antigen. In response to a sudden high-level infection risk (accidental inoculation with infectious material), persons whose immune status is uncertain should also be passively immunized with human anti-HBs antiserum—if possible within hours of pathogen contact.
It has not yet proved feasible to grow HBV in vitro. The antigen used in vaccinations can be isolated from human blood. Fear of AIDS infections has resulted in emotionally based, unjustifiable rejection of this vaccine. An alternative vaccine is now available based on developments in genetic engineering: the HBs antigen can now be synthesized by a yeast fungus.
Prevention: hepatitis B booster vaccines. Periodic booster shots, especially for persons at high risk, were recommended for some time to maintain sufficient immune protection. However, since all successfully vaccinated persons build up immunity rapidly following renewed contact with the pathogen ("immunological memory," see p. 94), this recommendation has been replaced in a number of countries by the following scheme:
Following immunization on the classic model (0,1, and 6 months), the anti-HBs antibody titer is measured within one to three months. Responders (titer 100 lU/l) require no booster. In hyporesponders and nonresponders (ti-
ter <100 IU/l), an attempt should be made to reach a titer of 100 IU/l with a maximum of three further vaccinations.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.